MAC

Question 1

MAC

Answer 1

minimum alveolar concentration
the lowest concentration of an anesthetic agent at which 50% of patients show no response to painful stimulus

Question 2

what is the relationship between MAC and potency of an anesthetic agent?

Answer 2

agents with low MAC are more potent

Question 3

what are the calculations for determining what percentage of an anesthetic agent to run?

Answer 3

1 x MAC = light anesthesia
1.5 x MAC = moderate anesthesia
2 x MAC = deep anesthesia

Question 4

what factors does MAC vary with?

Answer 4

age, body temperature, metabolic activity
disease, gestation, obesity can alter potency

Question 5

how do we usually run inhalant anesthesia compared to the value of MAC?

Answer 5

we usually run it higher than MAC
moderate anesthesia plane is ideal

Question 6

relationship between solubility and MAC

Answer 6

higher solubility = higher potency = lower MAC
lower solubility = lower potency = higher MAC

Question 7

what is the goal of using sedatives, opioids, muscle relaxers, etc along with anesthesia?

Answer 7

to lower MAC
we want moderate anesthesia plane with less inhalant anesthesia

Question 8

partition coefficient

Answer 8

solubility is expressed as partition coefficient which is the ratio of the concentration of an agent in 2 substances

Question 9

blood-gas partition coefficient

Answer 9

the ratio of the concentration of an inhalant agent in the blood and in the alveolar gas

Question 10

blood-gas partition coefficient relationship between solubility and blood/gas

Answer 10

poorly soluble = decreased blood/gas
highly soluble = increased blood/gas

Question 11

effect of low blood-gas partition coefficient on solubility

Answer 11

BGPC of 0.5 (low) indicates that anesthetic is 1/2 as soluble in the blood as it is in the alveolar gas
means that 2/3 of anesthetic is in the alveolar gas and 1/3 of it is in blood
ideal because we want more anesthetic in lungs so they wake up faster after

Question 12

effect of high blood-gas partition coefficient on solubility

Answer 12

BGPC of 2 (high) indicates anesthetic is twice as soluble in the blood as in the alveolar gas
means that 1/3 of anesthetic is in alveolar gas and 2/3 is in blood (hanging out in tissues)

Question 13

what does partition coefficient indicate?

Answer 13

it indicates the speed of induction, change of depth, and recovery expected for agent
lower BGPC = faster induction, change of depth, and recovery

Question 14

high partition coefficient relationship with solubility

Answer 14

high PC is highly soluble in blood and tissues
readily absorbed into blood and tissues
high levels don’t build up in alveolus = low concentration gradient - slow diffusion
high PC slow to leave tissues = slow recovery

Question 15

vapor pressure

Answer 15

amount of pressure exerted by gaseous form of a substance when the gas and liquid states are in equilibrium
equilibrium: # of molecules leaving liquid = # of molecules reentering
measure of an inhalant’s tendency to evaporate

Question 16

what is vapor pressure dependent on?

Answer 16

anesthetic agent and temperature

Question 17

how is high vapor pressure described as?

Answer 17

volatile
volatile agents must be delivered from precision vaporizer

Question 18

what vaporizer do you use with low vapor pressure agents?

Answer 18

they don’t require a precision vaporizer

Question 19

halogenated anesthetics

Answer 19

liquids at room temperature and turn into gas with O2
stored in vaporizers

Question 20

fresh gas

Answer 20

O2 + anesthetic

Question 21

halogenated anesthetics mode of action

Answer 21

inhibits nerve cell function in the brain and spinal cord, inhibits neurotransmitter-gated ion channels and gamma-aminobutyric acid (GABA) receptors, diffuses across alveolar cell membranes to blood stream

Question 22

how is the rate of diffusion of halogenated anesthetics controlled?

Answer 22

controlled by the concentration gradient between alveolus, bloodstream, and lipid solubility of drug

Question 23

effect of increased lipophilicity

Answer 23

increased lipophilicity –> increased ability to cross neuronal membranes –> increased potency

Question 24

how is anesthesia maintained?

Answer 24

with sufficient quantities of the agent in the blood, alveoli, and brain
decreased quantity administered —> decreased alveolar concentration —> reverses concentration gradience

Question 25

effects of halogenated anesthetics

Answer 25

CNS: dose related reversible depression
CV: depression, vasodilation, decreased cardiac output
resp: depress vasodilation (Vt and RR)

Question 26

adverse effects of halogenated anesthetics

Answer 26

CNS: increased ICP
CV: hypotension —> decreased renal blood flow
resp: hypoventilation —> increased CO2 —> respiratory acidosis

Question 27

isoflurane

Answer 27

most common inhalant anesthetic
approved for dogs and horses
high vapor pressure: 240 mmHg
vaporizer setting range: 0.25-5%
low blood-gas partition coefficient: 1.46
MAC ~1.3-1.6%
good for renal disease patients
mostly excreted through lungs and < 1% is metabolized/excreted through liver/kidneys
low PC so change in depth is quick

Question 28

sevoflurane

Answer 28

2nd most common inhalant anesthetic
used in dogs
vapor pressure: 160 mmHg
precision vaporizer required
blood-gas partition coefficient: 0.68
non-irritating and odorless
vaporizer setting range: 0.25-8%
MAC ~2.3-2.58%
less potent than iso = higher concentration needed
mainly excreted through lungs and 2-5% excreted through liver/kidneys

Question 29

desflurane

Answer 29

newest inhalant anesthetic
lowest blood-gas partition coefficient: 0.42
“1 breath anesthesia”
vapor pressure: 700 mmHg
boiling point: 74.3 F
used with a special electronic heated vaporizer
MAC ~7.2-9.8%
vaporizer setting range: 1-18%
mainly excreted through lungs and < 1% excreted through liver/kidneys